A nuclear reactor installation of the pressurized-water coolant type produces useful power via one or more steam generators each having a housing containing a heat exchanger through which the reactor coolant circulates. Such a heat exchanger commonly comprises an inverted U-shaped tube nest having inlet and outlet legs respectively connected to receive and discharge the circulating coolant.
The generator housing has, of course, a suitable steam output outlet and, normally in its lower portion, a feed water input connection supplied with feed water from a source which must provide a higher fluid pressure than the steam pressure in the generator's housing. The outlet leg of the heat exchanger may be provided with a preheater in the form of walls and baffles surrounding the heat exchanger's output leg and into which the feed water input connection opens, the feed water circulating around the output leg of the heat exchanger before entering the main body of water in the steam generator housing.
Such a preheater is normally designed with its various walls and baffles adequately capable of structurally resisting the forces caused by the normal flow of input feed water into the preheater. However, in the event a pipe line connecting the feed water source with the generator's feed water input connection, should fail and open the line pressure to the atmosphere, the steam pressure in the generator's housing produces a reverse flow of water backwardly through the input connection. This reverse flow is at a sufficient velocity to possibly cause damage to the walls and baffles of the preheater. The reverse flow rate created by the high-pressure steam behind the water, may provide forces sufficient to actually disintegrate the preheater, pieces of its construction then flying about within the steam generator's housing and possibly damaging the heat exchanger itself which is a construction that is very expensive. In addition, there is the danger that if the heat exchanger is damaged extensively enough, the reactor coolant may escape within the generator's housing and result in an extremely hazardous condition.
The object of the present invention is to provide a relatively inexpensive but thoroughly effective protective system for avoiding the above indicated possible consequences of a failure on the part of the feed water input supply line.